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                            <div style="color:gray; word-break: break-all; font-size:12px;">原英文版地址: <a href="https://www.elastic.co/guide/en/elasticsearch/reference/7.7/index-modules-merge.html" rel="nofollow" target="_blank">https://www.elastic.co/guide/en/elasticsearch/reference/7.7/index-modules-merge.html</a>, 原文档版权归 www.elastic.co 所有<br/>本地英文版地址: <a href="../en/index-modules-merge.html" rel="nofollow" target="_blank">../en/index-modules-merge.html</a></div>
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<strong>重要</strong>: 此版本不会发布额外的bug修复或文档更新。最新信息请参考 <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/index.html" rel="nofollow">当前版本文档</a>。
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<h2 class="title">
<a id="index-modules-merge"></a>Merge<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/elasticsearch/edit/7.7/docs/reference/index-modules/merge.asciidoc">edit</a>
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<p>A shard in Elasticsearch is a Lucene index, and a Lucene index is broken down
into segments. Segments are internal storage elements in the index where the
index data is stored, and are immutable. Smaller segments are periodically
merged into larger segments to keep the index size at bay and to expunge
deletes.</p>
<p>The merge process uses auto-throttling to balance the use of hardware
resources between merging and other activities like search.</p>
<h3>
<a id="merge-scheduling"></a>Merge scheduling<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/elasticsearch/edit/7.7/docs/reference/index-modules/merge.asciidoc">edit</a>
</h3>
<p>The merge scheduler (ConcurrentMergeScheduler) controls the execution of merge
operations when they are needed.  Merges run in separate threads, and when the
maximum number of threads is reached, further merges will wait until a merge
thread becomes available.</p>
<p>The merge scheduler supports the following <em>dynamic</em> setting:</p>
<div class="variablelist">
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<dt>
<span class="term">
<code class="literal">index.merge.scheduler.max_thread_count</code>
</span>
</dt>
<dd>
   The maximum number of threads on a single shard that may be merging at once.
Defaults to
   <code class="literal">Math.max(1, Math.min(4, Runtime.getRuntime().availableProcessors() / 2))</code>
   which works well for a good solid-state-disk (SSD).  If your index is on
   spinning platter drives instead, decrease this to 1.
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